U.S. patent application number 13/966370 was filed with the patent office on 2014-10-23 for cathode for lithium-air battery, method of manufacturing the same, and lithium-air battery comprising the same.
This patent application is currently assigned to Korea Institute of Energy Research. The applicant listed for this patent is Korea Institute of Energy Research. Invention is credited to Kyu-Nam Jung, JONG-WON LEE, Seung-Bok Lee, Tak-Hyoung Lim, Seok-Joo Park, Ahmer Riaz, Kyung-Hee Shin, Rak-Hyun Song, Su-Keun Yoon.
Application Number | 20140315105 13/966370 |
Document ID | / |
Family ID | 51729260 |
Filed Date | 2014-10-23 |
United States Patent
Application |
20140315105 |
Kind Code |
A1 |
LEE; JONG-WON ; et
al. |
October 23, 2014 |
Cathode for Lithium-Air Battery, Method Of Manufacturing The Same,
And Lithium-Air Battery Comprising The Same
Abstract
This invention relates to a cathode for a lithium-air battery, a
method of manufacturing the same and a lithium-air battery
including the same. The method of manufacturing the cathode for a
lithium-air battery includes 1) stirring a cobalt salt,
triethanolamine and distilled water, thus preparing a cobalt
solution, 2) electroplating the cobalt solution on a porous
support, thus preparing a cobalt plated porous support, 3) reacting
the cobalt plated porous support with a mixture solution including
oxalic acid, water and ethanol, thus forming cobalt oxalate on the
porous support, and 4) thermally treating the cobalt oxalate.
Inventors: |
LEE; JONG-WON; (Daejeon,
KR) ; Jung; Kyu-Nam; (Daejeon, KR) ; Shin;
Kyung-Hee; (Seoul, KR) ; Song; Rak-Hyun;
(Seoul, KR) ; Park; Seok-Joo; (Daejeon, KR)
; Lee; Seung-Bok; (Daejeon, KR) ; Lim;
Tak-Hyoung; (Daejeon, KR) ; Yoon; Su-Keun;
(Daejeon, KR) ; Riaz; Ahmer; (Daejeon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Korea Institute of Energy Research |
Daejeon |
|
KR |
|
|
Assignee: |
Korea Institute of Energy
Research
Daejeon
KR
|
Family ID: |
51729260 |
Appl. No.: |
13/966370 |
Filed: |
August 14, 2013 |
Current U.S.
Class: |
429/405 ;
205/57 |
Current CPC
Class: |
H01M 4/382 20130101;
H01M 2004/8689 20130101; Y02E 60/10 20130101; H01M 12/06 20130101;
Y02E 60/128 20130101; H01M 4/9016 20130101; H01M 4/8853 20130101;
H01M 12/08 20130101; Y02E 60/50 20130101; H01M 4/8621 20130101;
H01M 4/8807 20130101 |
Class at
Publication: |
429/405 ;
205/57 |
International
Class: |
H01M 4/86 20060101
H01M004/86; H01M 4/88 20060101 H01M004/88 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2013 |
KR |
10-2013-0044210 |
Claims
1. A method of manufacturing a cathode for a lithium-air battery,
comprising: 1) stirring a cobalt salt, triethanolamine and
distilled water, thus preparing a cobalt solution; 2)
electroplating the cobalt solution on a porous support, thus
preparing a cobalt plated porous support; 3) reacting the cobalt
plated porous support with a mixture solution comprising oxalic
acid, water and ethanol, thus forming cobalt oxalate on the porous
support; and 4) thermally treating the cobalt oxalate.
2. The method of claim 1, further comprising cooling a product
obtained in 4).
3. The method of claim 1, wherein a concentration of the cobalt
salt is 0.05.about.0.5 M based on the distilled water.
4. The method of claim 1, wherein a concentration of the
triethanolamine is 0.1.about.1 M based on the distilled water.
5. The method of claim 1, wherein the porous support is provided in
a form of foam, mesh or foil having holes.
6. The method of claim 1, wherein the electroplating is performed
at a current of 1.about.100 mA cm.sup.2.
7. The method of claim 1, wherein a volume ratio of the water
relative to the ethanol in the mixture solution is
0.01.about.0.5.
8. The method of claim 1, wherein a volume ratio of the water
relative to the ethanol in the mixture solution is
0.03.about.0.3.
9. A cathode for a lithium-air battery, comprising cobalt oxide
having a spinel structure.
10. The cathode of claim 9, wherein a shape of the cobalt oxide is
selected from the group consisting of a needle shape, a plate shape
and a flower shape.
11. A cathode for a lithium-air battery, manufactured using the
method of claim 1.
12. A lithium-air battery, comprising: the cathode for a
lithium-air battery of claim 11; an anode comprising lithium metal
or a lithium alloy; a separator disposed between the cathode and
the anode; and an electrolyte.
13. The lithium-air battery of claim 12, wherein the separator is
selected from the group consisting of glass fibers, polyester,
Teflon, polyethylene, polypropylene and polytetrafluoroethylene
(PTFE).
14. The lithium-air battery of claim 12, wherein the electrolyte
comprises a solvent and a lithium salt.
15. The lithium-air battery of claim 14, wherein the solvent is
selected from the group consisting of propylene carbonate, ethylene
carbonate, fluoroethylene carbonate, diethyl carbonate, ethylmethyl
carbonate, methylpropyl carbonate, butylene carbonate,
benzonitrile, acetonitrile, tetrahydrofuran,
2-methyltetrahydrofuran, .gamma.-butyrolactone, dioxolane,
4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide,
dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane,
dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate,
methylethyl carbonate, diethyl carbonate, methylpropyl carbonate,
methylisopropyl carbonate, ethylpropyl carbonate, dipropyl
carbonate, dibutyl carbonate, diethyleneglycol, dimethylether,
dimethyldiglycol, dimethyltriglycol and dimethyltetraglycol.
16. The lithium-air battery of claim 14, wherein the lithium salt
is selected from the group consisting of LiPF.sub.6, LiBF.sub.4,
LiSbF.sub.6, LiAsF.sub.6, LiClO.sub.4, LiCF.sub.3SO.sub.3,
Li(CF.sub.3SO.sub.2).sub.2N, LiC.sub.4F.sub.9SO.sub.3, LiSbF.sub.6,
LiAlO.sub.4, LiAlCl.sub.4, LiN(C.sub.xF.sub.2x+1SO.sub.2)
(C.sub.yF.sub.2y+1SO.sub.2) (wherein x and y are a natural number),
LiCl and LiI.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a cathode for a lithium-air
battery and a lithium-air battery comprising the same, and more
particularly, to a cathode for a lithium-air battery, which may
lower the charge voltage of a lithium-air battery, thus enabling
the lithium-air battery to have improved energy efficiency and
superior cycle life of charge and discharge, and to a method of
manufacturing the same and a lithium-air battery comprising the
same.
[0003] 2. Description of the Related Art
[0004] A lithium-air battery indicates a battery that uses lithium
(Li) metal as an anode and oxygen (O.sub.2) in air as a cathode
active material, and is a novel energy storage system able to
substitute for a conventional lithium ion battery. This lithium-air
battery is a battery system wherein oxidation/reduction of lithium
at an anode and reduction/oxidation of oxygen supplied from the
outside at a cathode occur and also wherein secondary battery and
fuel cell technologies are combined. The theoretical energy density
of the lithium-air battery is 11,140 Wh/kg, which is much higher
than those of other secondary batteries.
[0005] The lithium-air battery typically includes an anode, a
cathode, and an electrolyte and a separator between the anode and
the cathode. The cathode is typically composed of porous carbon and
a binder. However, the carbon material reacts with lithium peroxide
(Li.sub.2O.sub.2) produced during discharge of the lithium-air
battery, and promotes the decomposition of an organic electrolyte,
thus forming byproducts such as lithium carbonate
(Li.sub.2CO.sub.3), etc. Also, the binder used to manufacture the
cathode is known to decompose due to the reaction with lithium
peroxide. Thereby, the lithium-air battery is disadvantageous
because its charge voltage is very high and charge and discharge
energy efficiencies are remarkably low, and the life of the battery
is very short due to byproducts which continuously accumulate
during the cycle. Therefore, the development of a cathode able to
decrease the charge voltage of a lithium-air battery and to
increase the cycle life, without including carbon and a binder, is
required.
SUMMARY OF THE INVENTION
[0006] Accordingly, the present invention has been made keeping in
mind the above problems encountered in the related art, and an
object of the present invention is to provide a cathode for a
lithium-air battery, a method of manufacturing the same and a
lithium-air battery comprising the same, wherein cobalt oxide
having a spinel structure is used as a cathode, instead of porous
carbon and a binder which are typically used in the lithium-air
battery, thus lowering the charge voltage of the lithium-air
battery, thereby enabling the lithium-air battery to have improved
energy efficiency and superior cycle life of charge and
discharge.
[0007] The present invention provides a method of manufacturing a
cathode for a lithium-air battery, comprising 1) stirring a cobalt
salt, triethanolamine and distilled water, thus preparing a cobalt
solution; 2) electroplating the cobalt solution on a porous
support, thus preparing a cobalt plated porous support; 3) reacting
the cobalt plated porous support with a mixture solution comprising
oxalic acid, water and ethanol, thus forming cobalt oxalate on the
porous support; and 4) thermally treating the cobalt oxalate.
[0008] The method of manufacturing the cathode for a lithium-air
battery may further comprise cooling a product obtained in 4).
[0009] The concentration of the cobalt salt is preferably
0.05.about.0.5 M based on distilled water.
[0010] The concentration of the triethanolamine is preferably
0.1.about.1 M based on distilled water.
[0011] The porous support may be provided in the form of, for
example, foam, mesh or foil having holes.
[0012] The electroplating is preferably performed at a current of
1.about.100 mA cm.sup.-2.
[0013] The volume ratio of water relative to ethanol in the mixture
solution is preferably 0.01.about.0.5, and more preferably
0.03.about.0.3.
[0014] In addition, the present invention provides a cathode for a
lithium-air battery, comprising cobalt oxide having a spinel
structure.
[0015] The shape of cobalt oxide is preferably selected from the
group consisting of a needle shape, a plate shape and a flower
shape.
[0016] In addition, the present invention provides a cathode for a
lithium-air battery, manufactured using the above method.
[0017] In addition, the present invention provides a lithium-air
battery, comprising the cathode for a lithium-air battery as above;
an anode comprising lithium metal or a lithium alloy; a separator
disposed between the cathode and the anode; and an electrolyte.
[0018] The separator may be selected from the group consisting of
glass fibers, polyester, Teflon, polyethylene, polypropylene and
polytetrafluoroethylene (PTFE).
[0019] The electrolyte may comprise a solvent and a lithium
salt.
[0020] The solvent may be selected from the group consisting of
propylene carbonate, ethylene carbonate, fluoroethylene carbonate,
diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate,
butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran,
2-methyltetrahydrofuran, .gamma.-butyrolactone, dioxolane,
4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide,
dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane,
dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate,
methylethyl carbonate, diethyl carbonate, methylpropyl carbonate,
methylisopropyl carbonate, ethylpropyl carbonate, dipropyl
carbonate, dibutyl carbonate, diethyleneglycol, dimethylether,
dimethyldiglycol, dimethyltriglycol and dimethyltetraglycol.
[0021] The lithium salt may be selected from the group consisting
of LiPF.sub.6, LiBF.sub.4, LiSbF.sub.6, LiAsF.sub.6, LiClO.sub.4,
LiCF.sub.3SO.sub.3, Li(CF.sub.3SO.sub.2).sub.2N,
LiC.sub.4F.sub.9SO.sub.3, LiSbF.sub.6, LiAlO.sub.4, LiAlCl.sub.4,
LiN(C.sub.xF.sub.2x+1SO.sub.2) (C.sub.yF.sub.2y+1SO.sub.2) (wherein
x and y are a natural number), LiCl and LiI.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The above and other objects, features and advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0023] FIG. 1 illustrates the X-ray diffraction pattern of a
cathode manufactured in Example 1;
[0024] FIG. 2 illustrates a transmission electron microscope (TEM)
image of the cathode manufactured in Example 1;
[0025] FIG. 3 illustrates a scanning electron microscope (SEM)
image of the cathode manufactured in Example 1;
[0026] FIG. 4 illustrates a SEM image of a cathode manufactured in
Example 2;
[0027] FIG. 5 illustrates a SEM image of a cathode manufactured in
Example 5;
[0028] FIG. 6 illustrates a charge-discharge curve of a lithium-air
battery manufactured in Example 1;
[0029] FIG. 7 illustrates a charge-discharge curve of a lithium-air
battery manufactured in Comparative Example 1; and
[0030] FIG. 8 illustrates cycle properties (discharge
capacity-cycle number) of the lithium-air batteries of Example 1
and Comparative Example 1.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0031] Hereinafter, a detailed description will be given of the
present invention. In the description of the present invention, a
detailed description of the related known configurations or
functions may be omitted.
[0032] The advantages and features of the present invention and the
methods able to achieve them will be more clearly understood from
the following detailed description of the preferred embodiments
with reference to the appended drawings. However, the present
invention is not limited to the embodiments described herein but
may be embodied variously. The embodiments of the invention are
rather provided so that the disclosed contents become thorough and
complete and the spirit of the present invention may be
sufficiently transferred to those skilled in the art. For the sake
of clear description, the thicknesses of layers and regions in the
drawings are depicted to be exaggerated.
[0033] The terms used in this application are merely used to
express specific embodiments, and are not construed as limiting the
present invention. Unless otherwise stated, the singular expression
includes a plural expression. In this application, the terms
"include" and "have" are used to designate the presence of
features, numbers, steps, operations, components, parts or
combinations thereof described in the specification, not intending
to exclude the presence or additional possibility of one or more
different features, numbers, steps, operations, components, parts
or combinations thereof.
[0034] Unless otherwise defined, all the terms used herein
including technical or scientific terms have the same meanings as
those typically understood by those skilled in the art. The general
terms defined in dictionaries should be understood as meanings
which coincide with the meanings in the contexts of related
technologies, and are not construed as ideal or excessively formal
meanings, unless otherwise defined explicitly.
[0035] The embodiments described in this specification and the
configurations shown in the drawings are preferred embodiments of
the present invention, and do not represent all of the technical
ideas of the present invention and thus a variety of equivalents
and modifications able to substituted therefor may be provided at
the point of time of the present invention being filed.
[0036] According to the present invention, a method of
manufacturing a cathode for a lithium-air battery includes 1)
stirring a cobalt salt, triethanolamine and distilled water, thus
preparing a cobalt solution; 2) electroplating the cobalt solution
on a porous support, thus preparing a cobalt plated porous support;
3) reacting the cobalt plated porous support with a mixture
solution comprising oxalic acid, water and ethanol, thus forming
cobalt oxalate on the porous support; and 4) thermally treating the
cobalt oxalate.
[0037] In the method of manufacturing the cathode for a lithium-air
battery according to the present invention, a cobalt salt,
triethanolamine and distilled water are stirred, thus preparing the
cobalt solution (Step 1)).
[0038] Examples of the cobalt salt may include cobalt nitrate,
cobalt chloride, cobalt acetate, cobalt acetylacetonate, etc.
[0039] Triethanolamine enables the cobalt layer to be uniformly
plated, and triethanolamine adsorbed to the cobalt layer functions
to one-dimensionally selectively grow cobalt oxalate.
[0040] The cobalt salt preferably has a concentration of
0.05.about.0.5 M.
[0041] As such, if the concentration of the cobalt salt is less
than the above lower limit or exceeds the above upper limit, a
uniform cobalt plating layer cannot be formed, which is
undesirable.
[0042] The concentration of triethanolamine is preferably
0.1.about.1 M.
[0043] As such, if the concentration of triethanolamine is less
than the above lower limit or exceeds the above upper limit, a
uniform cobalt plating layer cannot be formed, and it is difficult
to prepare nano-structured cobalt oxalate and cobalt oxide.
[0044] Subsequently, the cobalt solution prepared in Step 1) is
electroplated on the porous support, thus preparing the cobalt
plated porous support (Step 2)).
[0045] The porous support may be provided in the form of a porous
structure, including foam, mesh, foil having holes, etc., using a
material such as metal having electronic conductivity, a polymer,
an inorganic material and so on.
[0046] The electroplating is preferably performed at a current of
1.about.100 mA cm.sup.2.
[0047] As such, if the current of the electroplating is less than
the above lower limit, the plating rate may become very low. In
contrast, if the current of the electroplating exceeds the above
upper limit, a uniform cobalt plating layer cannot be formed, which
is undesirable.
[0048] Subsequently, the cobalt plated porous support prepared in
Step 2) is reacted with the mixture solution comprising oxalic
acid, water and ethanol, thus forming cobalt oxalate on the porous
support (Step 3)).
[0049] The volume ratio of water relative to ethanol in the mixture
solution is preferably 0.01.about.0.5, and more preferably
0.03.about.0.3.
[0050] If the volume ratio of water relative to ethanol is less
than the above lower limit, it is difficult to manufacture a porous
structure. In contrast, if the volume ratio of water relative to
ethanol exceeds the above upper limit, the surface area of the
electrode may decrease, which is undesirable.
[0051] In this step, cobalt oxalate is produced via chemical
reaction between the cobalt ion dissolved from the cobalt plating
layer and the dissociated oxalic acid ion, and oxalic acid is not
dissociated in the form of an ion in ethanol but is dissociated
only in the presence of water. Also, the cobalt ion may be
dissolved from the cobalt plating layer only in the presence of
water. Hence, the extent of dissociation of oxalic acid and the
extent of dissolution of cobalt ion are determined depending on the
volume ratio of water and ethanol, and thereby the shapes of cobalt
oxalate and cobalt oxide may vary.
[0052] In the above mixture solution, the concentration of oxalic
acid relative to a mixture solution of water and ethanol is
preferably 0.05.about.1 M. If the concentration thereof is less
than the above lower limit, the surface area of the electrode may
decrease, which is undesirable. In contrast, if the concentration
thereof exceeds the above upper limit, it is difficult to
manufacture a porous structure, which is undesirable.
[0053] Subsequently, cobalt oxalate formed in Step 3) is thermally
treated (Step 4)). In this step, thermal treatment of cobalt
oxalate is preferably performed at 180.about.500.degree. C. for
0.5.about.5 hr in an air atmosphere.
[0054] Cobalt oxide having a spinel structure may be manufactured
using the above method, and cobalt oxide having a spinel structure
may be effectively utilized in manufacturing a cathode for a
lithium-air battery.
[0055] This cobalt oxide may have, for example, a needle shape, a
plate shape or a flower shape. The surface area and the internal
porous structure of the cathode may vary considerably depending on
the shape of cobalt oxide. In the case where cobalt oxide has the
above shape, the electrochemical active area for oxygen reaction is
the largest, and the number of pores in which Li.sub.2O.sub.2
formed upon discharge may accumulate is high, thus attaining the
greatest discharge capacity.
[0056] A lithium-air battery comprising the cathode as above may be
manufactured as follows.
[0057] The cathode of the present invention is manufactured as
mentioned above.
[0058] Subsequently, an anode is manufactured using an active
material such as lithium metal, a lithium alloy, etc. which are
typically used in the art.
[0059] The cathode and the anode may be separated by means of a
separator, and any separator may be used so long as it is typically
useful in a lithium battery. Particularly useful is a separator
having low resistance to ion movement of an electrolyte and high
electrolyte uptake.
[0060] The separator is selected from among, for example, glass
fibers, polyester, Teflon, polyethylene, polypropylene,
polytetrafluoroethylene (PTFE) and combinations thereof, and may be
provided in the form of nonwoven fabric or woven fabric.
Specifically, a separator which is rollable, such as polyethylene,
polypropylene, etc., or a separator having high organic electrolyte
uptake, may be used.
[0061] The electrolyte used in the lithium battery may include a
solvent and a lithium salt, and examples of the solvent may include
propylene carbonate, ethylene carbonate, fluoroethylene carbonate,
diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate,
butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran,
2-methyltetrahydrofuran, .gamma.-butyrolactone, dioxolane,
4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide,
dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane,
dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate,
methylethyl carbonate, diethyl carbonate, methylpropyl carbonate,
methylisopropyl carbonate, ethylpropyl carbonate, dipropyl
carbonate, dibutyl carbonate, diethyleneglycol, dimethylether,
dimethyldiglycol, dimethyltriglycol, dimethyltetraglycol, etc., and
examples of the lithium salt may include LiPF.sub.6, LiBF.sub.4,
LiSbF.sub.6, LiAsF.sub.6, LiClO.sub.4, LiCF.sub.3SO.sub.3,
Li(CF.sub.3SO.sub.2).sub.2N, LiC.sub.4F.sub.9SO.sub.3, LiSbF.sub.6,
LiAlO.sub.4, LiAlCl.sub.4, LiN(C.sub.xF.sub.2x+1SO.sub.2)
(C.sub.yF.sub.2y+1SO.sub.2)(wherein x and y are a natural number),
LiCl and LiI.
[0062] Subsequently, a separator impregnated with an electrolyte is
disposed between the cathode plate and the anode plate, thus
forming a lithium-air battery structure.
[0063] The lithium-air battery is suitable for use in fields
requiring high capacity, such as electric vehicles, and may also be
utilized in hybrid vehicles and so on by being combined with
conventional internal combustion engines, fuel cells,
super-capacitors, etc. Furthermore, the lithium-air battery may be
employed in other uses requiring high capacity, such as mobile
phones, portable computers, etc.
[0064] A better understanding of the present invention may be
obtained via the following examples which are set forth to
illustrate, but are not to be construed as limiting the present
invention, which is apparent to those skilled in the art.
Example 1
1. Manufacture of Cathode
[0065] Cobalt sulfate and triethanolamine were dissolved in
distilled water, thus preparing a mixture solution. As such, the
concentration of cobalt sulfate relative to distilled water was
0.26 M, and the concentration of triethanolamine relative to
distilled water was 0.53 M. As a porous support, a nickel foam was
adopted. The nickel foam was used as a working electrode, and a
platinum mesh was used as a counter electrode, and a current of 10
mA cm.sup.2 was applied for 250 sec, so that metal cobalt was
electroplated on the nickel foam from the above solution.
Subsequently, oxalic acid was dissolved in a mixture solution of
water and ethanol. As such, the volume ratio of water/ethanol in
the mixture solution was 0.1, and the concentration of oxalic acid
relative to the mixture solution was 0.3 M. The nickel foam plated
with metal cobalt was immersed in the mixture solution for 90 min,
and dried, thus manufacturing cobalt oxalate on the nickel foam.
The cobalt oxalate was brought into contact with dry air at
250.degree. C. for 2 hr so as to be thermally treated, and then
subjected to furnace cooling, thus manufacturing cobalt oxide on
the nickel foam.
2. Manufacture of Lithium-Air Battery
[0066] A lithium-air battery was manufactured using the cathode, a
lithium counter electrode, a glass fiber separator, and an
electrolyte having 1M Li(CF.sub.3SO.sub.2).sub.2N dissolved in
dimethyltetraglycol.
Example 2
[0067] A cathode and a lithium-air battery were manufactured in the
same manner as in Example 1, with the exception that the volume
ratio of water/ethanol in the mixture solution of oxalic
acid/water/ethanol was 0.03.
Example 3
[0068] A cathode and a lithium-air battery were manufactured in the
same manner as in Example 1, with the exception that the volume
ratio of water/ethanol in the mixture solution of oxalic
acid/water/ethanol was 0.05.
Example 4
[0069] A cathode and a lithium-air battery were manufactured in the
same manner as in Example 1, with the exception that the volume
ratio of water/ethanol in the mixture solution of oxalic
acid/water/ethanol was 0.3.
Example 5
[0070] A cathode and a lithium-air battery were manufactured in the
same manner as in Example 1, with the exception that the nickel
foam plated with metal cobalt was immersed in the mixture solution
of oxalic acid/water/ethanol for 60 min.
Comparative Example 1
Manufacture of Cathode
[0071] Carbon black (Denka Black) and a PVdF binder were mixed at a
weight ratio of 80:20, thus preparing a slurry. This slurry was
applied on a nickel mesh, dried at 80.degree. C. and then vacuum
dried at 120.degree. C., thus manufacturing a cathode plate.
[0072] (Manufacture of Lithium-Air Battery)
[0073] A lithium-air battery was manufactured using the cathode
plate, a lithium counter electrode, a glass fiber separator, and an
electrolyte having 1M Li(CF.sub.3SO.sub.2).sub.2N dissolved in
dimethyltetraglycol.
Test Example 1
X-Ray Diffraction Test
[0074] In order to evaluate the crystalline structure of the
cathode of Example 1, an X-ray diffraction test was performed. The
test results are shown in FIG. 1. As seen in FIG. 1, the cobalt
oxide cathode manufactured in Example 1 had a spinel structure, and
had neither a secondary phase nor an impurity phase.
Test Example 2
TEM test
[0075] In order to evaluate the shape and crystalline structure of
the cathode of Example 1, a TEM test was performed. The test
results are shown in FIG. 2. As seen in FIG. 2, a large number of
nanopores were present on and in the cobalt oxide. Also, the
manufactured cobalt oxide had a polycrystalline structure
comprising small crystal grains having a size of 2-5 nm.
Test Example 3
SEM Test
[0076] In order to evaluate the shape of the cathode of Examples 1,
2 and 5, a SEM test was performed. The test results are shown in
FIGS. 3 to 5. As seen in FIGS. 3 to 5, in the case where the volume
ratio of water/ethanol was lowered, the shape of cobalt oxide was
changed from a needle shape to a plate shape. Also, in the case
where the immersion time in the mixture solution of oxalic
acid/water/ethanol was decreased, the shape of cobalt oxide was
changed from a needle shape to a flower shape.
Test Example 4
Charge and Discharge Test
[0077] A charge-discharge test was performed using the lithium-air
batteries of Examples 1 to 5 and Comparative Example 1.
Specifically, discharge was performed up to 2.0 V at a constant
current of 20 mA/g, after which charge was performed up to 4.2 or
4.6 V at a constant current of 20 mA/g. As such, the applied
current density was calculated based on the weight of the
cathode.
[0078] FIGS. 6 and 7 illustrate the charge-discharge curves of the
lithium-air batteries of Example 1 and Comparative Example 1. As
such, the capacity was calculated based on the weight of the
cathode. The lithium-air battery of Example 1 using the cobalt
oxide cathode without carbon and a binder exhibited a lower charge
voltage, compared to that of Comparative Example 1. Table 1 below
summarizes the capacity, charge voltage and charge-discharge
efficiency of the lithium-air batteries of Examples 1 to 5 and
Comparative Example 1.
TABLE-US-00001 TABLE 1 Capacity, charge voltage and
charge-discharge efficiency of lithium-air batteries of Examples 1
to 5 and Comparative Example 1 Capacity (mAh/g) Charge voltage (V)
Energy efficiency (--) Ex. 1 2,280 3.88 71 Ex. 2 1,127 3.87 71 Ex.
3 1,846 3.89 71 Ex. 4 1,642 3.90 70 Ex. 5 1,930 3.92 70 Comp. Ex. 1
2,097 4.35 60
Test Example 5
Cycle Test
[0079] A charge-discharge cycle test was performed using the
lithium-air batteries of Example 1 and Comparative Example 1.
Specifically, discharge was performed until the capacity reached
500 mAh/g at a constant current of 100 mA/g, after which charge was
performed until the capacity reached 500 mAh/g at a constant
current of 100 mA/g. As such, the applied current density was
calculated based on the weight of the cathode.
[0080] FIG. 8 illustrates the capacity during the cycle test of the
lithium-air batteries of Example 1 and Comparative Example 1. The
lithium-air battery of Example 1 using the cathode without carbon
and a binder exhibited superior cycle properties compared to that
of Comparative Example 1.
[0081] Accordingly, the cobalt oxide cathode having a spinel
structure according to the present invention contains neither
carbon nor a binder which cause side reactions, thus improving the
energy efficiency and cycle life of charge and discharge of the
lithium-air battery.
[0082] As described hereinbefore, the present invention provides a
cathode for a lithium-air battery, a method of manufacturing the
same and a lithium-air battery comprising the same. According to
the present invention, the cathode for a lithium-air battery
includes cobalt oxide having a spinel structure, instead of porous
carbon and a binder which are typically used in a lithium-air
battery, thus lowering the charge voltage of the lithium-air
battery and increasing the cycle life of charge and discharge,
thereby improving energy efficiency.
[0083] The embodiments of the present invention have been disclosed
in the specification and drawings, and specific terms used herein
are merely regarded as general meanings to easily explain the
technical contents of the present invention and to aid the
understanding of the present invention, and are not construed to
limit the present invention.
[0084] Those skilled in the art will appreciate that the present
invention may be carried out in the other specific forms without
departing from the technical spirit or essential features thereof.
Accordingly, it is to be understood that the embodiments described
herein are illustrative and are not limited.
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